Optical projection apparatus



Jan. 29, 1935.

A. F. c, POLLARD 1,989,336

OPTICAL PROJECTION APPARATUS Filed. April 17, 1953 2 Sheets-Sheet l g4) F PO/LWZ pvven/mq Jan. 29, 1935. A. F. c. POLLARD 1,939,336

OPTICAL PROJECTION APPARATUS Filed April 1'7, 1935 2 Sheets-Sheet 2 Patented Jan. 29, 1935 PATE l ort'ricnr. PrtoJEcrIoNYAPP RaTUs.

Application npril 17, 1933, Serial No. 666,595

,, -'In. Great Britain July 15, 1932 3 Claims. (Cl. 88-24) The invention relates to optical projection apparatus and in particular tosky projectors for throwing letters, designs and so forth on the clouds for publicity or other purposes.

question comprises a source of light in the focus of a parabolic mirror-with a representation of the object to be projected, e. g.,' a stencil, disposed in a plane transverse. to the projected beam, an image .of the stencil'being formed by, helpof a "suitable lens system. J 5

This proposed apparatusinvolvesthe use of a large stencil incorrectly illuminated by more or less parallel light and is-necessarily unwieldy; and

cumbrous ,whilea considerable. lossof light oc- "curathereby decreasingthe illumination of the projected image. 3 v

.A main object of the present invention is to ob-. viate the above objections.

With such a main object, the invention consists;

in optical projection apparatus comprising the m inationsf lem nts ;-her ina ter describ d and particularly pointed out in the claims.

It will be understood that with the type of apparatus according to the present invention, it is essential for success that the axis of the conical beam of light reflected from the mirror should pass centrally through the operative part of the object and coincide with the axis of the lens system.

When an electric arc is used as the source of light with the positive carbon axially disposed with its crater towards the mirror, the image of the crater formed on the stencil may be a circular area of only some three inches diameter situated ten feet or thereabouts from the mirror and in such a case it is found impossible in practice to provide a mounting of such rigidity that relative displacements of the parts of the apparatus do not occur.

Thus, such a displacement, due to differential changes of temperature or other causes, even if comparatively slight may readily cause a small angular displacement of the mirror sufiicient to deflect the beam of light therefrom so that it is partly or wholly out of register with the object.

A particular object of the present invention is to overcome such difficulties.

Referring to the accompanying drawings, which are in part of a diagrammatic nature:

Figure 1 shows a sectional elevation of one form of the invention as a Whole, in which the mirror is of ellipsoidal form;

Figure 2 shows a side view of one of the units for tilting the mirror, while Figure 3 is'a section on the line 33 of Figure 2. In carrying the invention into effect according to one form as shown iii-Figure l, thesky projec-.

, tori apparatus comprises an elongated framework One proposed form of apparatus of the kind in v or casing, 2, mounted on trunnions, 3, about which it can be turned 'to different altitudes by a gear wheelA, engaging with a toothed sector, 5. The projector can also be moved in azimuthbyhelp of the hand-wheel, 6, actuating the toothed pinion, 7,'gearing with thefixed gear wheel, 8.

Any suitable locks or clamps may be provided to prevent accidental movement of the projector, e. g.,. ina cross wind; or again stops may be arranged where necessary to limit the movement of the projector in azimuth and so prevent tangling of the leads to the arc lamp hereinafter referred to. I r

The projector is provided with an ellipsoidal mirror, 9, details of the mounting of which will be described hereinafter, in the proximate focus of which is arranged the crater carbon, 10, of an are lamp, 11, having the usualfocussing'adjustments, products of combustion from the arc being withdrawn from the casing by means of a suction fan, 12.

The object, 13, to be projected, made of or depicted. on quartz or other refractory material, is arranged in the conjugate focus of the mirror, 9, whence the rays of light pass on through the lens system, 14, adjustable by the rack, 15, and pinion, 16. I

Since heat in addition to light is concentrated at the conjugate focus, the object, 13, and lens system, 14, may be cooled, if desired, by air from a fan, 17, driven for example by an electric motor, the air being led through a duct, 17a, within the casing to a jacket, 17b, surrounding the lens system,'apertures, 170, being provided in the wall of the duct in the neighbourhood of the object to be projected.

To secure critical illumination of the projected image, the major axis of the mirror, 9, and the optical axis of the lens system, 14, must be in line while the centre of the crater carbon, 10, and the object, 13, must be disposed on the same line; in addition the numerical aperture of the lens system must be equal to that of the mirror, or in other words, the lens system must be such as to receive the full expanding cone of light from the focus without diminution.

In order to-provide for an angular movement of the mirror, 9, about any axis in relation to the casing according to one plan, it is mounted on a ring, 18, from which project three equally spaced brackets, 19, each provided with a spherical facing, 20, with centre coinciding with the proximate focus of the ellipsoid. The spherical surface, 20, contacts (see Figures 2 and 3) with three or more spaced locating devices, each comprising a plate, 21, with slot, 22, secured to the casing, 2, the plate having an inclined face, 23, From the plate, 21, projects a lug,- 24, to which a bolt, 25, is secured at one end by the nut, 26,

I claim: 1. In combinationin optical apparatus for projecting images on clouds or other distant objects, a supporting framework and carried thereby a mirror, a source of light from which the rays of lightqare focused 9n the-object toabex projected, a lens-system disposed on the- SidOf said focus remote from the mirror, together with a jacket the other end of the bolt passing freely through i surrounding said lens system and means for cira slotted ear, 27, in which it is adjustable. long itudinally by the nuts, 28, 28, with spherical seats, 29, 29, arranged one on eachside-cfthe ear, 27:

The inclined face, 23, of the-plate, 21, co-acts by sliding its face, 31, along the fixed face, 23, until a surface, 33, on the angle v.piecewbears against the spherical surface, 20; the'angle piece, 32, can then be clamped in position by;a bolt, 34, passing through the slot, 22.

'By ,-;such means, any;angle of departureofthe mirron-from its properposition may be readily corrected and the image of the crater of the carbon maintained in its correct position on the opcal a s o t sy m,

As regards the objectf tojbe projected, this maytake the, form of a stencil-and; is preferablyv made of refractory, material since the heat concentrated, on the stencil is in general sufliciently intense ;to destroy stencils made of combustible material A suitable stencil consists of platinum foil suitably, perforated :to, produce the desired word or image-and the foil can be mountedin a holder, 35, slidable transversely in relation to the casing,, 2, in ,a suitable,guide,;36, or it can beiof tapeform ,and passed oversuitable spools and fed film-fashion through a gate locatedpin the ocalr ane Qft i s r e.

Various departHIS v:frQmthe constructions andprocesses describ ed above may :be made without exceeding thesc ope of theinvention: as defined inzthea jmszappendant hereto omittin coolingsair through said jacket, said 10 means including a duct leading to said jacket with at-Jeaswone outlet from said duct in the -neighbeurhcod-of=said object to be projected.

with a similarly inclined face, 31, =-;on an angle j piece, 32, which can be adjusted in'any position,

2. ln cornbinationjn optical apparatus for projec ting irnagespnclouds or other distant objects,

an ellipsoidal projector mirror, a mounting for ,said mirror,;-.saidimounting including circumfera entially-disposed parts having spherical surfaces with a, ,common centre at the near focus of said mirror, a projector framework carrying said mirror,, t0 ethe. i-w thsmea sz fomdiustin 'zthe p s tion f saidsmirrortran yer elyain relation to said projector ;;fram w.0rk,csaidameanssincludinggade ju abl wedgeelike memberainpperatiye .assochv ationarwithsaid csphericale surfaces. and:carniedby said projector frameworks.

3. In ,combinationrin :optical: apparatuszfonproec jectingimagesuon clouds orsotheri-d-istant objects, an ellipsoidal.,projecting mirrorwa mounting for said mirror,=.- said. i mounting including circum-- ferentially-disposed parts having spherica'lsur faces witha.common centre-atthe near focus of saidmirronia projectorframeworkicarrying said' mirror, and having -locating L members: in "opera---= tive association'- with -said :spherical surfacea to--- getherwith means for tilting said mirror-about-= any axis transverse to said projectonframeworb while maintaining saidoperative association-between said locating members and said 'spherical surfaces, 40

ALAN FARADAY OAMPBELBPOLEHARD'. 

